Recently, there is a growing attention paid to internal combustion engines of the spark-ignition cylinder-injection type.
JP-A 59-37236 discloses a fuel injection timing control for an internal combustion engine of the above kind. This engine performs an intake phase, a compression phase, a power phase and an exhaust phase and has a throttle valve in an air induction system that opens in degrees in response to depression of a gas pedal. According to this fuel injection timing control, information as to the engine rpm and information as to intake airflow rate are used in computing a base amount of fuel injection. In other words, the base amount of fuel injection is determined as a function of engine rpm and airflow rate and represents operator power requirement. The base amount of fuel injection is compared with a predetermined value. If the former is less than the latter, that is, power requirement is small, a table lookup operation of a two-dimensional table is performed based on engine rpm and airflow rate to determine an appropriate crankshaft position at which fuel injection should end. The base amount of fuel injection is converted into a fuel injector opening duration expressed in terms of crankshaft angles. These crankshaft angles are subtracted from the determined crankshaft position to give a result as a crankshaft position at which fuel injection should begin. Suppose the base amount of fuel injection is not less than the predetermined value, that is, power requirement is medium or large. In this case, a table look-up operation of another two-dimensional table is performed based on engine rpm and airflow rate to determine an appropriate crankshaft position at which fuel injection should begin. With this fuel injection timing management, stratified charge is formed to meet small power requirement, while homogeneous charge is formed to meet medium or large power requirement. The first mentioned two-dimensional table contains crankshaft angles ranging from 50.degree. BTDC to 100.degree. BTDC. The second two-dimensional table contains crankshaft angles ranging from 140.degree. BTDC to 330.degree. BTDC.
JP-A 3-281965 teaches performing a table look-up operation of a map in determining an appropriate spark timing for each of stratified charge combustion state and homogeneous charge combustion state.
Homogeneous charge combustion or stratified charge combustion is required to meet varying operating condition under which an internal combustion engine operates. Upon or immediately after a change, in request, from stratified charge combustion to homogeneous charge combustion, a special care has to be paid to the fact a fuel injection instant for homogeneous charge combustion be well in advance of an appropriate fuel injection instant for stratified charge combustion.
Thus, it is inevitable to allow at least one, if any, of cylinders to continue to perform stratified charge combustion immediately after the change, in request, to homogeneous charge combustion. With regard to such a cylinder that continues to perform stratified charge combustion, spark timing appropriate for homogeneous charge combustion Is adjusted to produce a spark to burn combustible charge resulting from the fuel injection in quantity and timing that are appropriate for stratified charge. This may result In incomplete combustion or occurrence of knock, causing increased emission of noxious components in the exhaust gas and a drop in derivability.
Therefore, it has been demanded that, immediately after a shift, in requirement, between stratified and homogeneous charge combustion, the ignition timing control as well as the fuel injection control switch, without any error, from stratified charge mode to homogeneous charge mode or vice versa form one individual cylinder to another.
Theoretically, it is possible to compute fuel injection quantity, fuel injection timing, and ignition timing appropriate for stratified charge combustion as well as those thru homogeneous charge combustion over the whole range of operation of the engine. In this case, operation time becomes long, increasing possibility that the engine controller might leave some of the jobs unfinished when the engine operates at high speeds.
An object of the present invention is to meet the above-mentioned demand.